The answer is that nobody knows because SSD's are too new to tell.

We played this game with optical media when it came out in the 80's and 90's, many claims were made about the longevity of various discs based on lab testing of accelerated aging, and now we know that simulating accelerated aging doesn't really cause the media to deteriorate in the way actual aging does.

There are all kinds of things that could go wrong with SSD's sitting there unpowered. As was mentioned, the cells lose charge over time and you get essentially bit-rot as they decay. If some part of the drive's firmware relies on a particular portion of data to exist on the flash memory and that has rotted away, well then that drive's now dead. Does this actually happen in practice? It'd be bad design, but we consumers have no way of knowing.

Likewise there are other things that can happen. Capacitors can degrade, tin whiskers can grow. All these things happen with solid-state electronics and cause them to fail over time.

SSD prices will likely rise in 2024. The market has been massively oversupplied, but they are reducing manufacturing to compensate. It will take some time to reflect in the MSRP but it's coming. Buy now while it's cheap!